Patent Document 1, for example, discloses a power source management system for an onboard device. When a user of an onboard device requires and a power source has power supply capacity, it enables remote control of the onboard device by supplying power to a communication device to enable communication. In contrast, unless the power source has power supply capacity although the user of the onboard device requires, it breaks the power supply to the communication device to reduce discharge of a vehicular battery as the power source.
In addition, an onboard multimedia device described in Patent Document 2 comprises at least one functional module that operates by the power supply from a power source, and an interface to which expansion equipment is connected. When new expansion equipment is connected to the interface and when the existing functional module that is present from before the connection includes an existing functional module corresponding to the functional module of the expansion equipment, it breaks the power supply to the existing functional module, and supplies power to the functional module of the expansion equipment.